Electric induction furnace



Jan. 24,1933. f

E. F. NoRTHRuP 1,895,421

ELECTRIC INDUCTION FURNACE Filed 001:. 7. 1929 Patented Jan. 24, 1,933

""uruTEn STATES PATENT OFFICE EDWIN FITCH NORTHRUP, OF PRINCETON, NEW JERSEY, ASSIGNOR TO AJAX ELECTRO- THERMIC CORPORATION, OF AJAX PARK, NEW JERSEY, A CORPORATION 0F NEW JERSEY ELECTRIC INDUCTION FURNACE f Application filed Octeber 7, 1929. XSerial No. 397,787.

My invention relates to-the protection of induction furnaces against injury to the furnaces or to those operating them by reason of leakage of molten metal through the furnace walls.

The main urpose of my invention isto provide a higiily refractory furnace lining to an inductor furnace coil which shall protect the coil from engagement by molten metal leaking from the furnace.

A further purpose is to provide an air dried refractory in intimate contact with a watercooled inductor furnace coil and of such character that it shall become sintered by contact With it of molten metal and shall thus protect the inductor coil from the met-al.

Further purposes will appear in the specification and in the claims.

I have preferred to illustrate my invention by but one form applied to a conventional furnace, selecting a form of illustration Which has been highly successful and which at the same time well illustrates the principles involved.

Figure 1 is a vertical, central section of a furnace showing an application of my invention.

Figure 2 is an enlarged fragmentary section corresponding to part of Figure 1.

In the drawing similar numerals indicate like parts.

Because my invention is applied to electric furnaces of the induction type it is necessary to illustrate it in connection with some such furnace. I have selected a standard type of furnace for this illustration Without intending to indicate that the invention is specially suited to the furnace shown and with knowledge that the invention is adapted for use with many other types of induction electric furnace.

lVhere Water-cooled inductor coils are used any leakage of molten metal against the coils becomes dangerous because of the. danger of explosion. Various efforts have. been made to prevent this by the use of crucibles and surrounding protective refractory. The recent practice of using a shell of sintercd refractory instead of a Crucible has increased the danger. Cracking of the Crucible or of this -shell -throws the molten metal against the heat insulation whose sintering must there' be reliedV upon to stop the flow. My invention is supplemental to whatever protection of this character may be provided and additionally protects the coil without interfering with the use of these existing protectivte means,

The furnace shown comprises a hase 5 of any refractory, such, for example, as silocel, upon which rests or is supported a furnace coil 6 which is Water-cooled in any suitable Way. In the form shown the Water cooling is accomplished by central inletand end outlet pipe connections 7, 8 and 9.

The invention well suited to the protection of water cooled coils for the reason that it can be Aapplied directly to or very close to the coils to be protected. It can be applied also to other coils,

.Inside the water-cooled coils I have shown a container lO which may be a separate crucible as shown and which is surrounded and heat-insulated hy finely dividing refractory l1 about the outside and below the Crucible. The top is completed and heat-insulated by suitable means such as asbestos in board or other form forming layers 12,13 and 14.

The finely divided refractory is ordinarily surrounded hy a shell of micanite 15 or other insulating material Which, at the time, alsov serves the. purpose of retaining the refractory material.

Thether such a shell of micanite or other material be used or not my invention consists in forming'a. protective layer of molded.

highly refractory, preferably air-dried cement between the coils and the layer of finely divided refractory. This shell 16 isrnost useful and, therefore. most desirable when plastered against the interior surfaces of the turns 17 of the inductor coil, and is shown as inserted between the turns and about the entire inner surface of the co'l.

This refractory cement is plastered upon the inside of the coil and may be formed of any highly refractory mixture which will air dry and which will bar any flow of leakage metal through it to the conductor coils.

Though I recognize that manyother Wellknown refractories will serve the purpose, and that even with the ingredients hereinafter described, the proportions may be greatly varied, in compliance with the requirement of the statute I give herein the composition of one mixture wh ch serves the purpose Well. I have used with great success a mixture of 70% sand, 20% alundum cement and 10% wet silicate of soda. It should be well mixed and is conveniently troweled in.

The mixture may be 'applied more eii'ectively to the coil if the portion of the coil to be covered be first coated with a sticky material which will cooperate with or blend with ithe cement. With the materials above I have used silicate of soda very satisfactorily. The lcovering of mixture need not be thick though there is no disadvantage from using a rather thick coating except as'it may involve 'increased spacing of the coil from the charge with consequent loss in coupling.

The coating-is dried and forms a mechanical protection for the inside'of the coil from the start. Because the shell formed is not brittle enough to crack the shell offers a complete sinterable refractory for engagement bythe molten metal leakage, fully protecting the coil.

It will be evident that an air-dried shell or shield is less frangible than one which is baked. The support oii'ered by the coil to the shell further protects the shell against mechanical injury.

It will be evident Vthat the position of the sinterable protective -shield adjacent to the coil spaces it suiiiciently from the furnace charge and cools it sufficiently by thev coil so lhat it will not be unduly hardened lby the eat.

It will befurther evident that this sintera-ble shield will perform its protective func tion independently of the character of the individual turns of the coil protected and of the type and extent of insulation Within and of the presence or absence cfa separate cruciyble. or sintered lining to hold the melt. l

It will be further evident that my invention is applicable to any type of lfurnace in which the coil is in danger of injury from -molten metal leakage flow, independently of the relative position of the coil and pool. f It will be further evident that the protective function of my shield is performed independently of the frequency and voltage of the current applied and is eective against leakage of both ferrous and non-ferrous metals. In case of leakage through the Crucible or sintered lining inmediately engaged by the melt the leakage metal first comes in contact sinters the shield or shell, which, being solid, stands up against the molten flow more effectively than does the loose refractory material.

Where I have referred to the lining as moulded I mean merely that a plastic material has been sha ed into the form desired and do not mean that the material need be re-formed. It is most desirably plastered in osition Within and between the turns.

have referred to airdrying to distinguish baking or sintering or to reduce danger from cracking While retainin the advantage of maintaining the materia in sinterable condition.

In view Yof my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art,

lto obtain all or part of the benefits of my invention without copyin the structure shown, and- I, therefore, clalm all such in so far as they fall within the reasonable spirit and scope of my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. In an induction electric furnace a furnace inductor coil and a solid sinterable lining shield adjacent to the coil.

able material and a finely divided sinterable 'j refractory between the lining and the charge.

5. In an induction electric furnace, a coreless furnace inductor coil, a solid unsintered lining adjacent the coil of sinterable material, a finely divided sinterable refractory between the lining and the charge and a crucible within the sinterable finely divided re fractory. 6. In an electric induction furnace a holder for molten metal, a finely divided refractory outside of the holder and adapted to be sintered by the adjacent molten metal with leakage of the metal, an inductor coil surrounding the refractory and an unsintered dried refractory molded against'the interior of the coil and in art surrounded by it.

EDWIN ITCH NORTHRUP.

with the finely divided refractory. A modcrate amount of leakage flow will be stopped by this, sintering. the refractory and automatically sealinigithe fracture. Where this is not sufiicient and the molten metal comes in contact with my shield or shell the metal 

